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UBC Theses and Dissertations

Some factors affecting the distribution and abundance of the chiselmouth (Acrocheilus alutaceus) Moodie, Gordon Eric Edmund 1966

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SOME FACTORS AFFECTING THE DISTRIBUTION AND ABUNDANCE OF THE CHISELMOUTH (ACROCHEHUS ALUTACEUS) by GORDON ERIC EDMUND MOODIE B.Sc., University of British Columbia, I964 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE In the Department of Zoology - We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1966 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agr e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r ex-t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n -c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f <fT" ° °^- ° The U n i v e r s i t y o f B r i t i s h C o l u m b i a Vancouver 8, Canada Date ~3~IAVW \~7 ISlaU i i ABSTRACT Some features of the biology of Acrochellus alutaceus were investigated with the purpose of explaining the rarity and disjunct distribution of the species in British Columbia. Two populations were compared, one in a lacustrine environment, in which the species is often rare, the other in a riverine environment, in which the species is usually common. Age and growth analysis of the two populations showed that in the river population growth continued for one year longer than in the lake population. Maximum age attained in both populations was .6 years,. Observations of feeding behavior in the field and laboratory suggested that the unusual lower jaw of the fish is an adaptation to scraping Aufwuchs, chiefly filamentous algae, from smooth substrates. Analysis of diet in the two habitats showed a much more restricted diet in the river. It is concluded that the growth of the type of food con-sumed by Acrocheilus and the occurence of a substrate suitable for feeding wi l l be most abundant and commonly found in warm rivers. The temperature required for spawning by Acrocheilus is probably higher than that of other local cyprinids* This may also limit the distribution of the species* In both habitats, diet changes with age| young fish lack the scraper-like lower jaw and eat principally insects,. Diatoms ingested with filamentous algae probably provide the chief source of nutrition D Filamentous algae undergoes l i t t l e or no digestive break-down. The possibility of interspecific competition for food and spawning sites in the lake is discussed. i i i TABLE OF CONTENTS page INTRODUCTION 1 THE STUDY AREA 2 THE MORPHOLOGY OF ACROCHELLUS . . . . . . . . . . . . . . . . . . 5 METHODS # 0 e , e o e o » o o o e 0 o o e o # 0 0 o o o o o o « * 5 TAXONOMY 0 0 0 © 0 O O 0 O * 0 O O 0 * 0 0 O O 0 O 0 O 0 O O O 0 9 SYNONOMY a o 0 O 0 o o * o 0 0 O 0 O 0 0 0 o o « 0 0 0 0 0 0 0 0 THE BIOLOGY OF THE CHISELMOUTH . 11 Dist ribut ion . . . o o . . . . . . . . 0 . O . . . . . O O 11 General Distribution 11 Local Distribution in the Wolfe Lake Study area . . t f o . o . o o . o . o o . . . . . 13 Local Distribution in the Okanogan River . . . . . 16 Aggressive Behavior . . . . . . . . . . 17 Age and Growth . . . . . . . . . . . . . . . . . . . . . 13 Parasitism and Disease . . . . . . . . . . 19 Reproduction . . . . . . . . . . . . o o o o . . . . . 21 Food and Feeding . . . . . . . . . . . . . . . . . . . . 25 The Method of Feeding of Acrocheilus . . . . . . . 25 The Time of Feeding of Acrocheilus . . . . . . . . 27 The Diet of Acrocheilus . . . . . . . . . . . . . . 27 The Digestion of Plant Material by Ac r ooh e ilus . . . . . . . . . . . . ' . o . o . . 28 The Abundance of Acrocheilus Relative to Ptychocheilus in Rivers and Lakes . . . . . . . . . . AO DISCUSSION o 0 0 0 . 0 0 0 0 0 o o o o O 0 0 O O 0 0 0 0 O O 0 o o CONCLUSIONS 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 50 LITERATURE CITED 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 52 i v LIST OF TABLES Table page I The number of different items eaten by adults of a given species i n Wolfe Lake which are not eaten by any other species compared to the number of items eaten which are also eaten by other species. Based on data of Tables I I I and IV.' "S" indicates food items shared by more than one species. "IF indicates items eaten only by that specieso . o . . . . . . . . . . . . . . . . . 33 I I The average amount of food.in the stomachs of adult A. alutaceus i n Wolfe Lake, from May through J u l y , and inthe Okanogan River, August 4 - 6 , 1965. Numbers indicate percent of t o t a l stomach capacity. n = s 3jnp3_6 SlLZG 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 * 0 33 I I I The diet of A. alutaceus, hybrid suckers, C. macrocheilus and M. 'caurinus adults i n Wolfe Lake. Numbers indicate percent composition of food items i n the gut, using the occurrence method of analysis . . . . 34 IV The diet of A. alutaceus, Ifybrid suckers, C. macrocheilus and M. caurinus adults i n Wolfe Lake. Numbers indicate percent composition of food items i n the guts using the point method of analysis. . . . . . . 35 V The diet of juvenile A. alutaceus, M. caurinus and P. oregonense and of both juvenile and adult R. baiteatus i n Wolfe Lake, June through July, 1965. Numbers indicate the percent composition of food In the guts, using the point method of analysis. .... . . . . . . . . . . . . . . 36 VI The diet of A. alutaceus i n the Okanogan River, August 4 - 6 , 1965, and i n the i n l e t stream of Wolfe Lake during the spawning period, 1965. Numbers indicate percent composition of food i n the guts, using the point method of analysis. . . . . . . . . . . . . . . . . . 37 V I I The r a t i o of A. alutaceus to P. oregonense i n lakes and r i v e r s . . . . . . . o o o o o . . . . . . . . . 41 V LIST OF FIGURES Figure page 1 The Wolfe Lake study area . . . . . . . . . . . . . . . . 4 2 A ground o t o l i t h , age three years . . . . . . . . . . . . 8 3 The d i s t r i b u t i o n of Acrocheilus and the extent of recent glac i a t i o n . . . . . . . o . . o o . . . . . . 12 4 The movement of marked and recovered chiselmouths i n Wolfe Lake. Recoveries made p r i o r t o the spawning period are indicated by "p.". Numbers indicate days between marking and recapture. Lack of a number indicates a f i n c l i p recovery, none of which were dated . . . . . . 14 5 Growth curve of Acrocheilus i n Wolfe Lake (closed c i r c l e s ) , based on 41 f i s h , and i n the Okanogan River (open c i r c l e s ) , based on 47 f i s h . Sexes are combined i n both curves. V e r t i c a l l i n e s indicate the range i n si z e v a r i a t i o n at ages one and two i n the r i v e r sample; sample sizes were 10 and 19 respectively. . . . . . . . . 20 6 An adult chiselmouth beginning t o feed. Note feeding scrapes i n the a l g a l mat . . . . . . . . . . o o . . . . 26 7 Marks produced by chiselmouths feeding on algae; A i n the laboratory with the algae growing on glass, B i n Wolfe Lake with the algae growing on a smooth log . . . . 26 8 The ontogeny of the lower jaw and of the c o i l i n g of the intestine of Acrocheilus. Drawings are not a l l t o the same sc 9 The diet of A. alutaceus,, M. caurinus„ G. macrocheilus t and hybrid suckers i n Wolfe Lake. V e r t i c a l axis indicates the percent composition of food i n the guts using the point method of analysis . . o o . a s o . o . o . o . . - 30 10 The diet of juvenile A. alutaceus,, M. caurinus, P. oregonense. and of both adult and juvenile R. balteatus i n Wolfe Lake. V e r t i c a l axis indicates the percent composition of food i n the guts using the point method of analysis o . o o o 0 o . . . o o o o o o 0 o o o o 0 . 31 11 The diet of adult and juvenile A, alutaceus i n the Okanogan River, August 4 - 6 , (A ,£ % 3), and of adults i n the i n l e t stream of Wolfe Lake during the spawning period (D). V e r t i c a l axis indicates the percent composition of food using the point method of analysis 0 0 0 0 0 0 . 0 . 0 0 0 0 . 0 0 0 . 0 0 0 . . 32 v i ACKNOWLEDGEMENTS I am grateful to Dr. C. C. Lindsey for suggesting the problem and contributing advice and supervision. Drs. J. F. Bendell, N. R. Liley, and T. G. Northcote critically read the manuscript and made many helpful suggestions. Mr. K. W. Stewart permitted the use of his data concerning hybrid abundances, spawning in Missezula lake, and his figure of chiselmouth gut morphology. His assistance in the field was also appreciated. Mr. K. R. Pitrie's enthusiastic help in the field was invaluable. V 1 J -INTRODUCTION This study deals with a freshwater cyprinid fish which is unique with regard to its scarcity and disjunct distribution. Acrocheilus alutaceus, commonly known as the chiselmouth, occurs In three drainage systems in north-western north America, the Fraser, Columbia, and Malheur systems (the last a closed drainage). Acrocheilus is present in both lakes and rivers, being reported most frequently from the latter. Agassiz and Pickering first described Acrocheilus from Willamette Falls and the Walla Walla River, Oregon (Agassiz, 1955). The fish was not discovered in British Columbia until 1950, in Skaha Lake (Ferguson 1950). Since then it has been taken in a few widely disjunct localities, and usually In small numbers. The distribution of the species in British Columbia is thus unusual and the population density relative to other cyprinids present is apparently low in a l l localities examined. The purpose of this study was to attempt to explain the unusual dis-tribution and abundance of Acrocheilus in British Columbia. The approach to the problem consisted of an investigation of the general biology of the species in order to discover whether it contained any features which might explain the distribution and abundance of the species. In particular, food and feeding, feeding behavior, age, growth and spawning requirements were examined. Where possible, these were studied on a comparative basis, examining a lake environment in British Columbia where the fish is scarce, and a river environment in Washing-ton where the fish is common. Food, spawning requirements, local distribution and fecundity of other cyprinids not showing the distribution of Acrocheilus were compared with Acrocheilus in order to see whether any differences might explain the peculiarities of the distribution and abundance of the chiselmouth. Most data were obtained during the summer of 19655 some samples were 2 procured on short field trips in the summer of 1964° THE STUDY AREAS / The main study area was Wolfe Lake (lat. 49° 26" N long, 120° 59' W), near the town of Princeton, British Columbia. This lake was chosen because of its accessability and relatively small size. Wolfe Lake is a shallow and roughly circular lake, with longest dimension 850 m, and surface area 33.6 hectares. It is the lowest of a chain of four lakes lying in a valley which was once the channel of the Similkameen River (Mathews, 1944). Wolfe Lake now drains via an outlet 1.3 km long into the Similkameen River (Fig. l ) . The west end of the lake is marshy, the margin in many parts consisting of Typha. Potamogeton is abundant in the open shallow water which is present only at this end of the lake. The lake has been dammed in recent times, causing the water level to rise approximately 1.2 m. As a result, the west end of the lake contains many submerged dead trees and bushes. The north and south shores are steeper than the west, consequently there is l i t t l e aquatic vegetation in this area. Windfallen logs are present above and below the surface. The lake empties over a rocky s i l l which is in part a r t i f i c i a l . The drop over the s i l l is probably an effective barrier to most species ascending the stream. The maximum depth found in the lake was 6.4 m. Thermal stratification was established in May, but was not strongly defined in May, June, or July, the duration of the study period. Frequent wind action probably prevents the es-tablishment of a stable stratification. The water is stained a deep brown color and contains large amounts of 3 s est on. Cyclopoid copepods make up the bulk of the zooplankton. Filamentous algae, epiphytic diatoms, chydorids, and gammarids are present in the littoral zone. Other fish in the lake are Ptychocheilus oregonense, (Northern Squaw-fish), Mylocheilus caurinus, (Peamouth Chub), Richardsonius balteatus, (Redside Shiner), Catostomus macrocheilus, (Largescale Sucker), Cyprinus cargio, (Carp), Prosopium williamsoni, (Mountain White-fish), and Salmo clarkii, (Cutthroat Trout). The last two species are uncommon. In addition there are suckers which are tentatively classified as hybrids between Catostomus columbianus, (Bridge-lip Sucker), and Pantosteus jordani, (Northern Mountain Sucker). These fish will hereafter be referred to as "hybrid suckers". The inlet creek enters the lake at the west end. The width of the creek is seldom more than 8 m, and the maximum depth less than 1.5 m. The average cross-section is about 4 m wide by 40 cm deep, the velocity in such an area in mid-June was 1.4 - 1.8 m per second. The bottom is made up of gravel of various sizes, distributed according to the velocity at a given area. The fast, deep zones have a bottom of large (10 - 20 cm) boulders. The area immediately beyond such a deep region is composed of much smaller ( 5 - 8 cm) rocks. Riffles are usually pebble-bottomed. Slow back-waters are sandy-bottomed. The entire lower part of the creek, just before i t enters the lake, is sandy-bottomed. The creek water is darkly stained and contains a large amount of suspended material. The flora of the creek consists of occasional patches of filamentous algae attached to rocks and logs. A fresh water sponge is common in the deep areas. Common insects in the creek are Ephemeroptera naiads and Trichoptera larvae. The margin of the.creek is densely overhung by Populus and small bushes. Beyond the ford (Fig. l ) , the gradient increases and there are few slower areas in which cyprinids can be found. Fish inhabiting the creek are Rhinichthys osculus9 (Speckled Dace), and Cottus rhotheus (Torrent Sculpin). 4 Figure 1. The Wolfe Lake study area 5 A sample of chiselmouths from a riverine population, was obtained from the Okanogan River near the town of Brewster, Washington, U.S.A., lat. 48° 10? N, long. 119° 45T W. The fish were collected in water ranging in depth from 0 - 2 m. The bottom consisted of large (15 - 25 cm) boulders, bearing a dense growth of filamentous algae and its associated Aufwuchs. The current was swift. Juveniles were obtained from sandy-bottomed shallow back-waters. Other species in the river habitat were R. baiteatus. C. macrocheilus, and P. oregonense. Only R. baiteatus was more abundant than Acrocheilus. Additional samples were obtained from Missezula Lake, Issitze Lake, Vidette Lake and Vaseux Lake, a l l in British Columbia. Small samples also were obtained from a few streams in central Washington. . THE MORPHOLOGY OF ACROCHEILUS The chiselraouth has an elongate, slightly compressed body. The maximum size is reported to be 300 mm. The caudal peduncle is narrow and the t a i l large and flaring. The most outstanding characteristic of the fish is its mouth. The snout overhangs the mouth, which is horizontal. The lower jaw bears a sharp, nearly square edge when viewed from beneath. The sharp part of the lip consists of cornified epithelium which is sometimes slightly calcified. Internal to the fleshy upper lip is a small, hard plate upon which the lower lip bears. Young fish have a more rounded lower lip, when viewed either laterally or frombelgw. The digestive tract is unmodified and is about twice the length of the body. METHODS Fecundity was estimated by a displacement method. The volume of the 6 j two ovaries was f i r s t measured by the displacement of k0% isopropyl alcohol In a graduate. The ovary was then broken up and enough eggs counted to displace one cubic centimeter of alcohol in a graduated centrifuge tube. This value was then multiplied by the t o t a l volume of the ovaries. Chiselmouth eggs were obtained from the inlet creek of Wolfe Lake in July of 1965. Females were stripped onto plastic screens, the eggs were then f e r t i l i z e d and taken to the laboratory. In the laboratory the eggs were placed in gauze baskets hanging in boxes with water circulating at a constant tempera-ture. Rearing temperatures were 12° and 18°C. The la r v a l fish were fed on brine shrimp nauplii and infusoria. Developing cyprinid eggs obtained directly from the spawning area in the inlet stream of Wolfe Lake, were reared in the same way. Behavior of the fish at spawning time, and the locations of the spawning areas in the inlet stream of Wolfe Lake were observed with the aid of a face mask and snorkel. In Wolfe Lake, adult fish were sampled for stomach contents analysis from May 7 through to July 20, I965. Sampling was carried on 24 hours per day, but the majority of the fish were caught during the night. The data presented thus represent almost daily small samples of Acrocheilus. Samples of other species and samples of juveniles of a l l species were obtained in the same places and during the same period of May through July, but at less frequent intervals. Adult fish were sampled with monofilament gillnets 2.4 m deep x 15.2 m long. Mesh size varied from 2 - 5 cm stretched. Juvenile fish were sampled by seining or, more commonly, by poisoning with rot en one. A l l specimens were i n i t i a l l y preserved in 10$ formalin, and later transferred to U0% isopropyl alcohol. Large fish were injected with formalin after capture. 7 For age studies otoliths were removed before fish were preserved in formalin. A transverse cut across the skull exposed the otoliths lying on each side of the brain. They were removed with forceps and stored in 50$ glycerin. For age determinations, the otolith was glued to a microscope slide, flat side down, using epoxy-resin. The slide was placed otolith down, on a glass plate which bore a paste of medium grade grinding compound and water. The otolith and surrounding resin were then ground down by rotating the slide. The progress of the grinding was frequently checked under a dissecting microscope, and the process stopped when the ground surface reached the level of greatest diameter of the otolith. The majority of otoliths treated in this way were readable (Fig. 2) . Those otoliths lacking distinct annular rings were discarded. Guts of Acrocheilus were left in the fish until the stomach content analysis was performed in the laboratory. Guts (and their contents) of species other than Acrocheilus were removed after capture, wrapped in gauze, identified and preserved in 10$ formalin. The composition of food eaten by a l l species was evaluated in two ways, each outlined by Hynes (1950). The volumetric method consists of the allotment of points, the total of which is based on the total volume of food in the gut. Since the stomach is very easily distended, the estimation of its degree of fullness is difficult, and only five classes of fullness are recognized? empty, i f u l l , J f u l l , $ f u l l , and completely f u l l . These conditions are given the following total number of points; 0, 5» 10, 15, 20 respectively. The points allotted on the basis of fullness are then proportioned according to the visually estimated proportions of the different food items in the gut. The second method consists of simply listing the food items as present or absent. This method does not take into account the abundance of the items in the individual fishes. The only departure from the methods of Hynes was that the entire 8 Figure 2. A ground o t o l i t h , age three years 9 i n t e s t i n a l t r a c t rather than only the stomach, was analyzed. The digestion of cellulose was examined by staining filamentous algae taken from different sections of the guts of chiselmouths with 75$ s u l f u r i c acid and IKI solution. This results In the cellulose membranes becoming blue. The amount of ce l l u l o s e present i n the c e l l walls of the algae was then estimated throughout the digestive t r a c t . Laboratory observations and photographs of feeding and other behavior were made in an aquarium measuring 145 cm long x 32 cm deep x 47 cm wide. A thic k growth of filamentous algae was produced on the sides of the aquarium by continuous illumination with three 100 watt l i g h t bulbs. The observer was con-cealed from the view of the f i s h by a clo t h screen and could watch the f i s h through a small opening. A l l f i s h observed were from Wolfe Lake. The d i f f i c u l t y involved i n obtaining and maintaining Acrocheilus resulted i n prolonged obser-vation of only f i v e individuals, three adults and two juveniles. One of these adults, maintained for 18 months, was the chief source of information concerning feeding behavior. Laboratory f i s h were fed primarily on commercially prepared trout food, although frozen brine shrimp were also used. Although given prepared food d a i l y the f i s h also fed frequently on the filamentous algae growing i n the aquaria. TAX0N0MT Acrocheilus alutaceus Agassiz and Pickering i s a cypriniform teleost belonging t o the suborder Cypriniodei, family Cyprinidae. Acrocheilus i s a monotypic genus. The occurrence of natural and a r t i f i c i a l hybrids between Acrocheilus and the other northern P a c i f i c slope cyprinids, Pbychocheilus  oregonense, Mylocheilus caurinus. and Richardsonius baiteatus a suggests that the differences among these genera may be less than t h e i r morphology would indicate. 10 SYN0N0MY Since a complete synonomy for Acrocheilus does not exist, i t was considered desirable to include one in this study., Acrocheilus alutaceum. Agassiz, L. Amer. Jour. Sci. Arts, 19$ 1859§99. Willamette Falls and Walla Walla River, Ore. Acrocheilus alutacium. Gunther, A. Catalogue of the fishes in the British Museum 1868; 7s1-512. Willamette Falls. Acrocheilus alutaceum. Jordan, D. S. Proc. U. S. Nat. Mus., 1879s ls69-85. John Day River. Acrocheilus alutaceum. Jordan, D. S. in Goode, G. B. The fisheries and fishery industries of the U. S. Fishes S ect. 1 Part 3» 616-618. Willamette Falls. Acrocheilus alutaceum. Bean, T. H. Proc. U. S. Nat. Mus., 1882; 5s89-93. Umatilla River, Walla Walla River. Acrocheilus alutaceum. Gilbert, C. H. and B. W. Evermann, Bu l l . U. S. Fish. Comm., 1894s 14s169-204. Tucannon River,. Grande Ronde River, Yakima River, Lower Crab Creek, Rock Island Dam, Wenatchee River, L i t t l e Spokane River, Hangman River. Acrocheilus alutaceum. G i l l , T. Smiths. Misc. Co l l . 1907s 48s297-340. Acrocheilus alutaceum. Snyder, J. 0. Bull . U. S. Bur. Fish., 1907s 27s 153-189. Clackamus River. Acrocheilus alutaceum. Snyder, J. 0. B u l l . U. S. Bur. Fish., 1907s 27s69-102. Sylvies River. Acrocheilus alutaceus. Ferguson, R. G. Can. Field Nat., 1950s 6 4 s l 5 6 . Skaha Lake. Acrocheilus alutaceum. Carl, G. C , W. A. Clemens and C. C. Lindsey. The fresh-water fishes of B r i t i s h Columbia. 1959s 117-119. Euchiniko River, Nazko River, Missezula Lake, Nicola Lake, Skaha Lake, Gallagher Lake, Tugulnuit Lake, Okanagan River, Windermere Lake, Wolfe Lake. 11 Acrocheilus alutaceum. Patten, B. (>. Copeia, 1960j l?71-73. Yakima River. Lavinia alutacea. Girard, C. Proc. Acad. Nat. Sci. Phila. 8, 1857s 165-213. Willamette River and tributaries. THE BIOLOGY OF THE CHISELMOUTH DISTRIBUTION General Distribution The distribution of Acrocheilus is noteworthy in that in the southern portion of its range it is a common fish, both In terms of overall distribution and of abundance relative to other species (Gilbert and Evermann, 1894)• In the northern part of the range i.e. British Columbia, Acrocheilus is rare in every sense (Fig. 3) . Since being found in Skaha Lake, Acrocheilus has been taken in several other lakes nearby. The nearest location to the above where chiselmouths occur is Wolfe Lake and Issitze Lake, 80 km to the west. Forty-five km to the north of these two lakes, chiselmouths are again found in Missezula Lake. Acrocheilus has not been found anywhere else in the Columbia system in British Columbia except for Windermere Lake, near the headwaters of the Columbia. In the Fraser system, chiselmoiiths are found in five localities. They have been taken in Vidette and Mara Lakes, which are about 90 km apart. Seventy-four km south of Vidette Lake, chiselmouths are found in Nicola Lake. The only other records of Acrocheilus in the Fraser system are from the Nazko and Euchiniiko Rivers, about 600 km northwest of Vidette Lake. Many of the intervening waters have been extensively sampled in the past 15 years, so that i f chiselmouths do occur in such localities they must be rare. In British Columbia, Acrocheilus is most often found in lakes rather than rivers. In Washington and Oregon, the reverse is the case. This may be correlated with the general scarcity of slow 'masring, warm, fairly eutrophic 12 Figure 3« The d i s t r i b u t i o n of Acrocheilus and the extent of recent g l a c i a t i o n 13 r i v e r s In B r i t i s h Columbia as compared t o Washington and Oregon. Local D i s t r i b u t i o n and Movement i n the Wolfe Lake Study Area The l o c a l d i s t r i b u t i o n and movement of Acrocheilus i n Wolfe Lake were studied for two reasons. F i r s t l y , an indication that the chiselmouth i s t e r r i t o r i a l would lend weight to the conclusion based on laboratory observations that the f i s h are aggressive, which i n turn would be of interest i f i n t r a s p e c i f i c competition for food occurs. Secondly, i f i n t e r s p e c i f i c competition for food occurs, i t i s necessary to know whether the different species occupy the same mic ro^hab i t at. In order to discover whether the chiselmouth occupies a home range, f i s h were i n d i v i d u a l l y marked at different points around the margin of the lake. The study was complicated by the spawning period which lasted from about June 10 t o July 9, i n 1965. Eighty-one f i s h , adults of both sexes, were marked with numbered aluminum c l i p s placed on the operculum. One hundred more were marked by clippi n g various combinations of f i n s . The maximum number of fins clipped on a f i s h was two. Marking was done from May 7 to June 9» 1965. Netting for recovery was conducted 24 hours per day, from May 7 to July 20, 1965» Marking was done at a variety of points around the margin of the lake. Netting for recovery was done • at the points of marking and at intervening points. Of the t o t a l marked by either method only 14 were recovered. The low recovery rate was probably due to injury sustained by the f i s h during g i l l n e t t i n g p r i o r t o i n i t i a l marking. Fish brought back to the laboratory were found to be extremely susceptible to disease even following the most careful handling. Recoveries and controls held i n the lake a f t e r tagging indicated that the tag i t s e l f seldom caused death. Figure 4 indicates the movements of marked f i s h which were recovered. It can be seen that i n the few instances where the f i s h were recovered p r i o r to 1 4 I i f 0 320 : Figure 4» The movement of marked and recovered chiselmouths i n Wolfe Lake. Recoveries made p r i o r to the spawning period are indicated^by? P N ° Numbers indicate days between marking and recapture. Lack of a number indicates a f i n c l i p recovery, none of which were dated. 15 the spawning migration, the amount of movement was l i m i t e d . In order to obtain further information about the movements of c h i s e l -mouths i n the lake, g i l l n e t s were set i n various patterns; Nets were set per-pendicular to shore with one end on or very close to shore. The depth of water was about 2 m near the shore and from 3 - 5 m at the offshore end of the net. The nets were always set with the lead l i n e on the bottom of the lake. This was the usual arrangement of nets throughout the study period May 7 t o July 20, 1965. with some exceptions to be noted. The direc t i o n of f i s h caught i n such an arrangement was almost equally divided, that i s one h a l f the f i s h were going i n either d i r e c t i o n . Fish were occasionally caught together but most often appeared t o be moving as individuals rather than i n groups. Except for two occasions at spawning time, there was never any suggestion that Acrocheilus adults swim i n schools. On 5 occasions 4 nets were set perpendicular to shore, but o f f the shore. Unless set within 6 m of shore, no chiselmouths were caught. In these cases the inshore end of the net extended from the surface to the bottom of the lake. On a separate occasion an equal number of nets were set p a r a l l e l t o shore. Again, unless the net was within 6 m of the shore, no chiselmouths were caught. In both cases nets were set i n a variety of places known to provide chiselmouths by other methods of capture. To discover whether movement along the shore was l i m i t e d , 4 nets were set p a r a l l e l t o each other 15 m apart and perpendicular to the shore, to which one end was attached. In such an arrangement the catch of the inner two nets was most often equal t o that of the outer two. This method of net setting was carried, out 4 times i n 2 locations. The t o t a l catch of t h i s as w e l l as any other arrangement usually diminished over a period of time. The results of the net catches indicate that the movement of adult Acrocheilus from May to July i s lim i t e d i n i t s along-shore component. 16 From May to July and on September 12 and 13, 1965, chiselmouths were found only around the margin of the lake, except for during the spawning period when they were in the inlet stream. On October 20, no Acrocheilus could be caught around the margin of the lake, but two were caught in deep water near the center of the lake, where they were never found earlier in the year. This suggests that in the autumn Acrocheilus either becomes very inactive or moves to deeper water. Young chiselmouths, up to age one, were obtained by dip-netting, seining and poisoning. The fish were found in mixed schools of young P. Oregonense0 M. caurinus, and R. baiteatus. Acrocheilus from 2 - 4 years of age were obtained by gillnetting. They were found most often with M. caurinus, and to a lesser extent, P. Oregonense of the same size. Adult chiselmouths were caught with a l l of the above species plus C. macrocheilus. On two occasions, just after the spawning period in Wolfe Lake and just prior to spawning in Missezula Lake, a large school of 50- 100 adult chisel-mouths was caught, in both cases the schools were not near the spawning area. Local Distribution in the Okanagan River The local distribution of adult chiselmouth in the river habitat, although examined only briefly, was different from that in Wolfe Lake. In the river adult chiselmotifch were more spatially isolated from each other and from other species, as determined by gillnet catches. Adults were, spaced out over the bottom and other cyprinids were rare in the area. Juveniles were caught using seines and glllnets and were found with the same species with which they occur in Wolfe Lake. 17 Aggressive Behavior The significance of aggressive behavior i n i n t e r s p e c i f i c competition and t e r r i t o r i a l i t y was explained e a r l i e r . The different l o c a l d i s t r i b u t i o n i n the lake and r i v e r examined suggested that i n the lake crowding might increase the extent of aggression t o a harmful degree. Laboratory observations of aggressive behavior were made on f i v e i n -dividuals. Observations were made on three adult f i s h i n the large aquarium previously described. I n i t i a l l y one adult was placed i n the tank. After several days, another f i s h approximately one cm larger was introduced. The introduced f i s h was immediately chased by the e a r l i e r inhabitant of the tank. Whenever the newcomer approached within about 45 cm of the other, i t would be driven back to the f a r end of the tank. While chasing, the aggressive f i s h would swim along side of and s l i g h t l y behind the other f i s h . Frequently the dominant f i s h would b i t e the region behind the dorsal f i n . After about.8 hours of such behavior, a glass divider was placed i n the center of the aquarium and was l e f t i n place for two days. Upon removal of the di v i d e r , the relationship between the two f i s h was reversed, the larger f i s h became the dominant and pursued the s l i g h t l y smaller f i s h when i t approached within about 45 cm. The f i s h were l e f t together and the;behavior described above was frequently "observed during the next three days. At the end of the t h i r d day, the smaller f i s h died, apparently due i n part t o an open wound behind the dorsal f i n , caused by the actions of the larger f i s h . One other adult of si m i l a r size to the dominant was placed i n the tank several days lat;er. When the previously described behavior began t o appear, the f i s h were permanently separated. ' Two juvenile f i s h were placed simultaneously i n an aquarium measuring 27 cm wide x 30 cm high x 50 cm long. The sizes of the f i s h were approximately 70 and 80 mm. The larger f i s h chased the smaller f i s h whenever i t approached with i n about 10 cm. As i n the case of the adults, chasing consisted of swimming 18 t o the side of and s l i g h t l y behind the f i s h being pursued. Less b i t i n g was observed i n the juveniles and the f i s h were uninjured a f t e r three days when they were separated. When placed i n adjacent aquaria of the dimensions given above, one f i s h frequently pushed against the side of the tank where i t could see the f i s h i n the other aquarium. The f i s h i n the second aquarium avoided the part of the aquarium closest to the other f i s h . This behavior was observed for f i v e days. These f i s h were aged about two years, one year more than those observed schooling i n the f i e l d . Chasing was also exhibited by an adult chiselmouth towards a juvenile peamouth chub. Whenever the chub l e f t i t s sheltering place, (a pane of glass set against the side of the tank), the chiselmouth pursued i t . This behavior persisted as long as the f i s h were together, a period of 18 months. AGE AND GROWTH Because of the difference i n abundance of Acrocheilus i n the lake and the r i v e r , i t was thought that an analysis of the age and growth of the species i n these two environments might indicate whether the growth rate i n the lake was reduced, thus indicating less favorable conditions. Otoliths were used to age Acrocheilus, since scales showed i n d i s t i n c t c i r c u l i . Samples large enough for ageing by the size frequency method could not be obtained. The o t o l i t h s were examined using epi-illumination and a black background. The usual magnification was 50X. The narrow annuli appear transparent i n contrast t o the whiteness of the broad intervening zones ( F i g . 2). Fish i n the r i v e r population having one and two annuli on t h e i r o t o l i t h s came from two d i s -t i n c t size classes, smallest and second smallest respectively. This was used t o establish the f i r s t year mark and as evidence that the annuli do i n fact represent yearly growth marks. The range of v a r i a t i o n and sample size of these two age 19 classes i n the r i v e r population are given i n Figure 5. The chief area of d i f f i c u l t y i n interpreting ages was i n the most recent part of the o t o l i t h i . e . at the margin. However the sector i n which the growth rings are most compressed was generally readable. About 40$ of the o t o l i t h s prepared were unreadable either because of improper mounting and/or grinding or because the annuli were not d i s t i n c t enough to make a confident estimate possible. I f there was any doubt as to the age of an o t o l i t h , i t was not used for the growth rate estimates. Forty-one f i s h from Wolfe Lake and 47 from the Okanogan River were aged. Growth curves for Acrocheilus from Wolfe Lake and the Okanogan River populations are shown i n Fig. 5« The maximum age attained i n both populations i s 6 years. The growth rate of the Okanogan River population i s greater than that of the Wolfe Lake population; t h i s difference i s highly s i g n i f i c a n t (F » 18.35» df 1, 83)« In the lake population, females reach a greater size than males of the same age, a f t e r the age of three. It i s not known whether the same holds i n the r i v e r population since sex determinations made in the f i e l d were l a t e r found to be unreliable. In Wolfe .Lake, males probably spawn at age 3> females probably spawn sometimes at age 3 but usually at age 4» PARASITISM AND DISEASE The p o s s i b i l i t y of disease and parasitism as a factor co n t r o l l i n g population density has been suggested by some authors (Mayr, 1963). Chiselmouths from both the lake and the r i v e r environment were examined for macroscopic para-s i t e s of the digestive t r a c t , coelom, and integument. On t h i s basis, the l e v e l of parasitism i n Acrocheilus i n both environments was lower than i n any of the other cyprinids examined, and was equalled only by the sucker C. macrocheilus. The only parasites seen were small nematodes which occurred i n low numbers i n the intestines of a few f i s h . Rarely one or two leeches were attached to the roof of the buccal cavity. No chiselmouth showing obvious signs of disease were 20 240 -i 40-20-i i — 1 : , , , 0 1 2 3 4 5 6 AGE (YEARS) Figure 5« Growth curve of Acrocheilus i n Wolfe Lake (closed c i r c l e s ) based on 41 f i s h , and i n the Okanogan River (Open c i r c l e s ) based on 47 f i s h . Sexes are combined i n both curves. V e r t i c a l l i n e s indicate the range i n si z e v a r i a t i o n at ages' one and two i n the r i v e r sample; sample sizes were 10 and 19 respectively. REPRODUCTION The spawning habits of Acrocheilus were examined i n Wolfe and t o a lesser extent, Missezula Lakes, i n order t o see whether there were any peculiar requirements which might l i m i t the d i s t r i b u t i o n of the species i n B r i t i s h Columbia, by preventing reproduction. In Wolfe Lake Acrocheilus undergoes a considerable spawning migration, some f i s h t r a v e l l i n g 1.5 km up the i n l e t stream. Chiselmouths began t o congregate at the mouth of the i n l e t stream June 10, 1965, and became rare i n the lake at t h i s time, '^ipe males were present i n the lake beginning on May 28. Ripe females appeared i n the i n l e t area June 20, at t h i s time the surface water temperature of the i n l e t area at mid-day was 17.8°C. Dis t r i b u t i o n of f i s h i n the creek was determined by almost d a i l y under-water observations during the spawning period. Observations were made at selected points i n the lower part of the creek between the bridge and the lake (Fig . l ) . On one occasion the entire creek from Is s i t ze Lake to Wolfe Lake was examined. .Gillnets were set i n the creek throughout the spawning period. Due to the rapid current, these were not f u l l y effective and permitted most f i s h to pass. (Fish observed between two nets were often seen to leave the area without being caught i n either net.) By June 23 chiselmouth were up t o 91 m upstream from the lake, i n the i n l e t creek. By June 26 f i s h had reached the ford and few or none went beyond t h i s point. Observations of tagged f i s h indicated that once i n the creek the f i s h probably remain several days, sheltering under brush p i l e s and log jams. The spawning migration of Acrocheilus i s much more extensive than that undertaken by the other cyprinids i n the lake. Both Ptychocheilus and Mylocheilus move only about 700 m upstream. The majority oi the redside shiners spawn i n the r i f f l e s near the lake. These cyprinids as w e l l as C. macrocheilus spawn s l i g h t l y before Acrocheilus. By July 9 f i s h were being caught i n a l l parts of 22 the lake again. Chiselmouths i n both Wolfe and Missezula Lakes did not spawn u n t i l the water temperature was approximately 17°C i n 1965 and also i n 1964 In Missezula Lake. This compares with minimal known spawning temperatures of 12.2°C for R. baiteatus, 4»5°C for M. caurinus, and 14.0°C for P. oregonense (C. C. Lindsey, pers. comm.). Eggs of Acrocheilus were found i n two locations i n the i n l e t t o Wolfe Lake. At the upstream s i t e , only a few scattered eggs were seen. Judging by the color, some of these were probably chiselmouth eggs. At the lower s i t e , a large number were found at the downstream end of a narrow pool about 9 m long, 3 m wide and 75 cm deep. Water depth over the eggs was about 30 cm. One side of the pool was l i n e d with a large tangle of dead branches and trees, the other side was a sandy bank. The eggs were adherent to a rock about 5 cm i n diameter and t o smaller ( l cm) stones. The bottom of the stream was devoid of macroscopic organic material either l i v i n g or dead. The egg mass was quite compact and was completely covered by a layer of 7.5 - 10 cm rocks. How the eggs are deposited i n such a location i s unknown. The extent to which R. baiteatus fed on exposed eggs indicates that eggs deposited on the open bottom would have a low s u r v i v a l rate. The eggs were eyed when discovered and the surrounding gravel contained many hatched larvae. When exposed to l i g h t and current, the larvae attempted to wriggle down into the gravel. About 100 eggs from the lower s i t e were sent back t o the laboratory for rearing. Of these, 80 grew to an i d e n t i f i a b l e s i z e ; 14.3$ of these were c h i s e l -mouths, the remainder were squaw f i s h . Actual spawning of Acrocheilus was not seen. Extensive observations were made, t o t a l l i n g many hours, both above and below the surface. As long as the observer did not approach any closer than 2 m, the f i s h did not seem disturbed. 23 Feeding and current-oriented behavior wasfioted but no behavior of a reproductive nature was seen. The conclusion must be either that Acrocheilus w i l l not spawn when an observer i s nearby, or else, as was the case with R.' bait eatus i n Wolfe Lake, chiselmouths spawn at dusk or i n the dark. The mean egg count for 6 chiselmouths was 6200. This compares with a range of 5000 t o 53,000 for Ptychocheilus (Cartwright, 1956). Eggs when l a i d are a d i s t i n c t i v e golden yellow color. Chiselmouth eggs obtained by stripping the parents hatched i n the laboratory i n 16 days at 12°C and In 6 days at 18°C, s l i g h t l y warmer than the creek temperature at spawning time. Eggs reared at 12°C a l l died within 35 days of f e r t i l i z a t i o n . At hatching the larvae, are about 8.1 mm long. The yolk i s orange-gold and elongate, running back to the anus. Chromatophores are present dorsally from between the eyes to a point midway between the dorsal f i n f o l d and the anus. A row of chromatophores also runs along the l i n e where the body meets the yolk sac. The following ch a r a c t e r i s t i c s were observed which serve to d i f f e r e n t i a t e Acrocheilus larvae from those of Ptychocheilus, the only other cyprinid l i k e l y to be spawning at the same time and place as Acrocheilus i n Wolfe and Missezula Lakes: - Blood i n the heart of Acrocheilus i s v e r m i l l i o n , as opposed to crimson i n Ptychocheilus. - Acrocheilus has more melanophores i n the anterior-dorsal region. - The yolk, sac of Acrocheilus i s longer, wider, rounder and reaches further forward than that of Ptychocheilus. - The yolk of Acrocheilus i s orange-gold, that of Ptychocheilus pale yellow. b Once the yolk has been absorved, i t i s impossible to d i f f e r e n t i a t e larvae of Acrocheilus from those of other cyprinids, u n t i l they reach a size of about 15 mm. At t h i s s i z e , the f i s h may be stained with a l i z a r i n and the f i f t h pharyngeal arch removed for i d e n t i f i c a t i o n by tooth count. The pectoral fins appear very early i n development, the pelvics much l a t e r . Primordia of the pelvic fins appeared i n laboratory reared f i s h at 47 days, at 18°C. The median f i n f o l d i s s t i l l present at 63 days at t h i s temperature. The ch a r a c t e r i s t i c short, downcurved mouth does not begin to appear u n t i l the f i s h reaches a size of about 15 mm. In Missezula Lake the i n l e t stream i s cold (10.5°C) i n mid-summer. Only Oncorhyncus nerka i s known to spawn there. Acrocheilus spawns i n an area of the lake just above the outlet. As i n Wolfe Lake, chiselmouths become rare i n t h e i r usual habitat during the breeding season and become concentrated i n the spawning area. In two years, ripe f i s h have been found only i n t h i s part of the lake. The actual area where eggs were deposited was not found. Acrocheilus were frequently observed under dense submerged and over-hanging bushes, a location i n which they were never found during the non-reproductive season. Water depth i n t h i s region was 25 100 cm, the bottom resembled that of the spawning area i n Wolfe Lake, being clean and composed of rocks from 1-15 cm i n s i z e . Except f o r the near absence of a current i n the Missezula Lake spawning area, i t was si m i l a r to that of the spawning area, i n Wolfe Lake. I s s i t z e Lake, above Wolfe Lake, was v i s i t e d June 3 0 , 1965, while spawning was taking place i n Wolfe Lake. The i n l e t stream was much colder than that of Wolfe Lake, however ri p e individuals of R. baiteatus. P. oregonense. M. caurinus. and C. macrocheilus were found i n the stream, presumably spawning. Acrocheilus was not found here nor i n the lake proper. Chiselmouths were seen i n the outlet stream, however, which was much warmer (17°C). Chiselmouths, adult and juvenile, were present for about 180 m downstream. It i s probable that spawning occurs i n the outlet. Acrocheilus was l a t e r found i n the lake i n September. An observation by J. D. McPhail (pers. comm.) at Omak Creek, Washington, indicates that r i v e r populations of Acrocheilus may u t i l i z e small t r i b u t a r i e s i n which t o spawn. 25 FOOD AND FEEDING This aspect of the study was given special emphasis since i t was'con-sidered that the unusual lower jaw of the species might be accompanied by special ecological requirements. The Method of Feeding of Acrocheilus Observations i n the laboratory and the f i e l d revealed that the sharp lower jaw of the adult chiselmouth i s used as a scraper t o remove Aufwuchs from the; substrate. . When feeding i n the large aquarium i n the laboratory, the.adult c h i s e l -mouth swims about 10 - 15 cm above the substrate. The t a i l i s then f l i c k e d powerfully, the head i s lowered and the f i s h slides i t s open lower jaw along the substrate (Fig. 6), The distance the jaw travels while scraping i s short, about 2 - 2 . 5 cm. The f i s h usually swims about b r i e f l y before repeating the procedure. Only rarely did the f i s h scrape the substrate for a distance greater than that given above. When such prolonged scraping occurs, the f i s h swims along and works the upper and lower jaws together i n what resembles a nibbling motion. Fish fed from v e r t i c a l , horizontal surfaces of the aquarium as w e l l as from large rocks. In a l l cases, the manner of feeding was si m i l a r . In the case of v e r t i c a l surfaces, • ' : . • • • v- . . . . . the f i s h approached the surface head-on, then t i l t e d the body head upward to about a 45° angle before making,the t y p i c a l feeding movement. Alte r n a t i v e l y , the f i s h would swim p a r a l l e l t o the v e r t i c a l surface and then r o l l on i t s side to scrape. In a l l cases, the feeding scrape i s accomplished by a sudden f l i c k of the t a i l which propels the f i s h against the substrate with considerable speed and results i n some Aufwuchs being removed from a short section of the substrate. In the i n l e t creek of Wolfe Lake chiselmouths were observed feeding i n a manner quite s i m i l a r t o that seen i n the laboratory aquarium. The f i s h i n the creek, which were adult spawners, were continuously swimming to maintain t h e i r 26 Figure 6. An adult chiselmouth beginning to feed. Note feeding scrapes i n the a l g a l mat. Figure 7. Marks produced by a chiselmouth feeding on algae; A i n the laboratory with algae growing on the glass about \ natural s i z e . B i n Wolfe Lake with the algae growing on a smooth log, about l/lO natural s i z e . 27 p o s i t i o n ; feeding therefore was intermittent. The f i s h would dart toward the creek bed about 10 cm beneath i t , scrape material from the substrate and then resume i t s position-maintaining a c t i v i t y . Figure 7 shows scraping marks made by Acrocheilus i n the f i e l d and i n the laboratory aquarium. A. log i n the creek was seen which bore many scrape marks. The log formed a spillway at a con s t r i c t i o n i n the creek, thus the ve l o c i t y of the water going over i t was high. It i s noteworthy that Acrocheilus can. feed i n such an environment. The Time of Feeding of Acrocheilus • Due to the d i f f i c u l t y of catching f i s h during daylight, i t was not possible t o get enough stomachs for t h i s time period to make a r e l i a b l e estimate of time of feeding. The. low catch rates during daylight are thought to be a result of v i s u a l net avoidance rather than sedentary.behavior during the day-l i g h t hours. This, b e l i e f i s supported by the fact that i n t u r b i d Wolfe Lake, the daytime catch rate was much higher than i n clear Missezula Lake. On the basis of brain morphology and the method by which Acrocheilus feeds, i t seems*very l i k e l y that i t i s a daylight feeder. M i l l e r (1965) showed that i n catostomids different types of feeding behavior may be correlated with development of•different areas of the brain. The configuration of the brain of Acrocheilus resembles that figured by M i l l e r of a v i s u a l l y oriented cyprinid. This i s t o be expected i n view of the fact that Acrocheilus appears t o locate i t s food v i s u a l l y . The Diet of Acrocheilus The diet of Acrocheilus was examined i n the r i v e r and the lake i n order t o see whether the same food was u t i l i z e d , and to find out whether there was any appreciable overlap i n the diet of Acrocheilus and of other cyprinids and catostomids i n the lake. 28 The diet of the chiselmouth changes with age (Figs, 10 and l l ) . Mo digestive t r a c t s were examined between the stage after absorption of the yolk and a length of 20 mm. From 20 - 100 mm the chiselmouth eats large amounts of insects. Beyond 100 mm Acrocheilus eats plant material, c h i e f l y filamentous algae, the percentage of which steadily increases with age (Figs, 9» 10, 11), The change i n diet can be correlated with the development of a coiled gut and a square, sharp-edged lower jaw, which becomes more pronounced with age ( F i g , 8 ) 0 The Digestion of Plant Material.by Acrocheilus-It can be. seen from--Tables'-III and IV that plant material i s an important component of the diet of Acrocheilus, It was of interest to learn whether Acrocheilus i s able to digest t h i s material. In nearly a l l the f i s h examined which contained plant material, eg, filamentous algae, i t was noted that there was l i t t l e or no evidence of digestive breakdown. Algae near the rectum was of the same color and condition as that at the anterior, end of the stomach. The c e l l u l a r contents of algae near the rectum were indistinguishable from those i n the stomach. Tests for cellulose (M, S. Weint'raub, pers. comm.) were made on algae from the stomach, midgut, and hindgut. In a l l cases,, there was no detectable reduction i n the amount of cellulose along the length of the gut. In the absence of ce l l u l o s e digestion, the f i s h would have to physically rupture the c e l l w a l l i n order to u t i l i z e the c e l l contents. There was no evidence that t h i s was done by'any s i g n i f i c a n t extent. It must be concluded then, that Acrocheilus derives l i t t l e or no n u t r i t i o n from filamentous algae, i n spite of i t s abundance i n the digestive t r a c t . Diatoms, which are on the 'average taken i n volume, equal to filamentous algae, are probably the chief source of n u t r i t i o n . The c e l l w a l l of diatoms, although i t s e l f indigestable, contains minute pores which expose the c e l l contents 1 30 Ul u < < l 80-60-40-20-MAY JUNE JULY 10 cr u u g oc co >-i 80-60-40-20-I n pa i BOTTOM ORGANISMS'-ORGANIC DEBRIS DIATOMS FILAMENTOUS ALGAE CHIRONOMID LARVAE MOLLUSCS NOSTOC COLONIES BRYOZOA ROCK PARTICLES i/) _J I d I U o cr U < (Jl 80 60-40-20-J _ i _ INTERMEDIATE ORANISMS: TRICHOPTERA LARVAE EPHEMEROPTERA NAIADS CRUSTACEA COPEPODS CHYDORIDS GAMMARIDS CLADOCERA OSTRACODS DAPHNIA Z IT < 80-60-40-SURFACE ORGANISMS: CHIRONOMID PUPAE LEMNA INSECTS 20-11 I Figure 9» The diet of A, alutaceus f l M. caurinus» C» macrocheilus 0 and hybrid suckers i n Wolfe Lake. V e r t i c a l axis indicates the percent composition of food in-the guts using the point method of analysis. 31 JUNE JULY UJ U < h-D _l < <l 80-60-40-20-J UJ to z UJ z o o UJ cr O 80-60-40-20-I . 1 I. 1 I H I I B O T T O M O R G A N I S M S : ORGANIC DEBRIS DIATOMS F I L A M E N T O U S ALGAE CHIRONOMID LARVAE tu < Z cr < 80-60-40-20-80-60-40-20-1 I 1 I I N T E R M E D I A T E ORGANISMS: TRICHOPTERA LARVAE CRUSTACEA COPEPODS CHYDORIDS DAPHNIA OSTRACODS INVERTEBRATE EGGS SURFACE O R G A N I S M S : CHIRONOMID PUPAE INSECTS La. Figure 10. The diet of juvenile A. alutaceus 9 M. caurinus. P. oregonense, and of both adult and juvenile R. baiteatus i n Wolfe. Lake. V e r t i c a l axis indicates the percent composition of food i n the guts using the point method of analysis. 32 100-90-I • i A <50 MM B 50-100MM C >100MM D >100 MM I BOTTOM ORGANISMS: DIATOMS FILAMENTOUS ALGAE ROCK PARTICLES SURFACE ORGANISMS: INSECTS Figure 11. The diet of adult and juvenile A„ alutaceus i n the Okanogan River, August 4-6, (A£B£'C), and of adults i n the i n l e t stream of Wolfe Lake during the spawning period (D) 0 V e r t i c a l axis indicates the percent composition of food using the point method of analysis. 33 Table I. The number of different items eaten by adults of a given species i n Wolfe Lake which are not eaten by any other species compared to the number of items eaten which are also eaten by other species. Based on data of Tables I I I and IV. " S " indicates food items shared by more than one species. "U" indicates items eaten only by that species. A. alutaceus C. macrocheilus M. caurinus Hybrid suckers S U S U S U S u May ••"7 2 '•' 5 3 8 1 . 9 0 June 6 • 2 .•; . 3 6 2 5 0 July 6 2 y •  6 4 2 3 . 6 0 Table I I . The average amount of food : in the stomachs of adult A. alutaceus i n Wolfe "Lake, from May through J u l y , and i n the Okanogan River, August 4 - 6, 1965. Numbers indicate precent of total :stomach capacity, n = sample siz e . May June July August ". 8 6 . 1 n = .'42 61,2 60 43 .1 77 55.4 44 34 Table IIT. The diet of A. alutaceus, hybrid suckers, C. macrocheilus and M. caurinus adults i n Wolfe Lake. Numbers indicate percent composition of food items i n the gut, using the occurrence method of analysis A. alutaceus Hybrid suckers C. macrocheilus M. caurinus May June July May June July May June July May June July Organic 21.3 27.0 22.9 23.8 29.4 22.2 ,'42.8 36.6 28.6 9.7 25.0 debris Diatoms 29.0 3 0.4 23.9 23.8 29.4 27.8 28.6 31.7 14.3 11.0 6.2 16.0 Filamentous 25.125.9 28.7 14.3 23.5 17.1 11.3 algae • Lemna 10.9- 4.1 1.1 • 17.1 12.5 Rock ^ 1.2 p a r t i c l e s Insects 3.8 3.5 2.6 9.5 5.5 4.9 5*7 ' 14.6 12.5 Chironomid 6.5 2.8 9.6 9.5 1111 4.9 5.7 14.6 larvae • Chironomid , 1.6 .2.8 9.6 pupae Trichoptera 0.6 1.2 larvae Ephemeroptera 1.1 3.6 6.2 naiads ... Crustacea : 5.9: :: 1.4 2.4 5.7 6.2 Copepods 8.6 Chydorids . 4.8 5.7 7.3 14.3 Grammarids / 4.8 5.9 4.3 2.4 26.8 25.0 4.0 Cladocera 77117.3 5.7 7 - 0 Ostracods 4.8 1.4 Daphnia 11.1 2.4 5.7 72.0 Fish eggs 4.0 Molluscs 6.2 4«0 Bryozoa 2.8 Nostoc colonies 1.2 Sample size 55 64 77 7 10 15 30 18 17 37 16 27 35 Table IV. The diet of A. alutaceus, Hybrid suckers, C. macrocheilus and M> caurinus adults i n Wolfe Lake. Numbers indicate percent composition of food items In the guts using the point method of analysis A, alutaceus May June July Hybrid suckers May June July C. macrocheilus M. caurinus May June July May June July Organic debris Diatoms Filamentous algae Lemna Rock p a r t i c l e s Insects Chironomid larvae Chironomid pupae Trichoptera larvae 24.5 24.3 17.5 24.2 17.4 12.1 61.5 53.9 30.0 17.1 15.0 32.1 34.S 22.5 27.1 28.0 33.2 9.3 4.3 0.2 0.8 0.9 3.0 2.0 3.8 2.9 11.3 0.4 2.0 12.4 0.1 0.7 32.8 39.4 35.6 18.0 22.9 10.1 11.6 1.8 5.4 Ephemeroptera 1.7 naiads Crustacea Copepods Chydorids Gammarids Cladocera Daphnia Ostracods Fish eggs Molluscs Bryozoa Nostoc colonies 3.9 3.9 10.1 6.7 0.9 0.8 8.6 17.4 20.1 6.2 13.9 16.0 14.8 7.1 2.0 1.7 2.0 9.4 19.0 1.4 3.3 3.7 20.1 11.0 4.9 2.0 10.0 3.6 3.0 2.9 1.6 0.8 14.0 11.3 3.2 9.8 23.9 4.6 2.6 30.8 34.O 3.1 1.7 5.5 2.0 1.3 12.3 93.8 0.5 0.3 2.0" 1.5 8.2 Sample size 55 64 77 7 10 15 30 18 17 37 16 27 36 Table V. The diet of juvenile A. alutaceus, M. caurinus and P. oregonense and of both juvenile and adult R." baiteatus i n Wolfe Lake, June through July, 1965. Numbers indicate the percent composition of food i n the guts, using the point method of analysis Organic debris Diatoms Filamentous algae Insects Chironomid larvae Chironomid pupae Trichoptera larvae Crustacea Copepods Chydorids Cladocera Daphnia Ostracods Invertebrate eggs A, alutaceus M. caurinus P. oregonense R. batteatus June July June July July July June July 14.2 27.5 4.4 1.6 5.6 65.2 6.8 2.2 18.2 9.9 21.5 15.5 5.1 1.2 18.1 9.4 2.3 41.9 29.4 2.5 6.2 6,2 18.7 6.2 57.5 2.5 3.5 3.3 1.1 19.1 42.9 8.8 2.2 4.2 3.1 9.7 3.0 3.3 4.0 4.0 2.7 1.0 34.0 26.3 37.3 25.0 7.3 8.0 14.3 30.0 8.7 16.0 30.0 16.0 1.7 13.3 3.3 10.7 Sample size 35 33 13 34 12 12 10 37 Table VI. The diet of A. alutaceus i n the Okanogan River, August 4-6, 1965. Numbers indicate percent composition of food i n the guts, using the point method of analysis. Diatoms Filamentous algae Rock p a r t i c l e s Insects 50 mm 0.8 0.6 98.6 Fork length 50 - 100 mm 22.1 5.8 3.9 69.1 100 mm 48.9 30.6 14.5 6.6 Sample size 19 11 49 The diet of adult A. alutaceus i n the i n l e t stream of Wolfe Lake during the spawning period, 1965. Diatoms Filamentous algae Rock p a r t i c l e s Insects Organic debris Lemna Chironomid larvae 30.2 47.2 10.2 0.8 10.7 0.8 0.1 Sample size 13 38 t o the environmento Because of t h i s construction, digestive enzymes i n the gut of Acrocheilus have ready access to the c e l l contents,, That t h i s occurs i n Acrocheilus i s evidenced by the fact that diatoms i n the stomach usually con-tained t h e i r c e l l contents, while diatoms i n the hihdgut consisted only of empty frustules (shells)., This diet i s very s i m i l a r to that of T i l a p i a esculenta, which feeds on planktonic filamentous algae and diatoms but digests only the diatoms (F i s h , 1951)<> The diatoms were v i r t u a l l y a l l of the Pennate group,, Diatoms consumed by Acrocheilus were always associated with filamentous algae upon which they are epiphytico This was not necessarily the case with diatoms eaten by other species. "Organic debris" referred t o i n Tables I I I , IV, V, and VI, i s a general term used to indicate a v a r i e t y of material which could not be p o s i t i v e l y i d e n t i f i e d . It i s thought, on the basis of microscopic examination, to consist to a large extent of u n i c e l l u l a r algae, and protozoa, and to a lesser extent of o i l droplets, c e l l contents of digested diatoms and bottom sediments. The bulk of i t i s probably epiphytic f l o r a and fauna associated with filamentous algae. Its n u t r i t i v e value i3 unknown. "Insects" referred to i n Tables I I I , TV, V, and VI, includes prim a r i l y adult winged forms which had been ground by the pharyngeal teeth to such an -extent that they could hot be further i d e n t i f i e d . Lemna was apparently taken deliberately by both Acrocheilus and M. caurinus, however i t did not undergo noticeable digestion i n either species. The diets of the species examined are shown i n Figures 9» 10, and 11 and Tables I I I , TV, V, and VI. The importance of an item i n terms of i t s percent contribution to the t o t a l food volume of the sum of a l l guts examined i s given on the v e r t i c a l axis. : Figures 9, 10, and 11 are based on data obtained by the points method of analysis. Differences i n the values obtained using the two methods of analysis are probably due either to small sample sizes i n a few cases, or t o 39 d i f f i c u l t y i n estimating r e l a t i v e volumes of many small organisms, especially when the organisms are intermingled. As Hynes (1950), Thompson (1959)# and others have noted, no method of gut analysis i s free from s u b j e c t i v i t y . As the s i z e of the gut decreases, the problems are compounded. Hynes also notes that as the sample size increases most of the different methods give comparable r e s u l t s . In t h i s study the two methods gave comparable results i n most cases, at least i n terms of r e l a t i v e abundance of the major items. For future discussion certain comments can be made at t h i s time about the food items. Diatoms, organic debris, and filamentous algae i f present i n a species can be considered to have been taken as a single item. The f i r s t two Items are almost never found separately, and algae i f present i s with the diatoms and debris. The remainder of the items show much more independence of each other. It can be seen from Tables III and IV, that adult A. alutaceus, C_. macrocheilus, M. caurinus and hybrid suckers i n many cases feed on the same items. The number of items eaten only by a single species i s f a i r l y low i n a l l cases. Acrocheilus "shares" a l l of i t s major food items (with one exception i n J u l y ) . Hybrid suckers "share" a l l items. It appears that t h e i r trophic s p e c i a l -i z a t i o n has been lo s t as a result of hybridization. Acrocheilus does not show the tendency displayed by C. macrocheilus and M. caurinus t o increase the number of unshared items as the summer'progresses (Table I ) . P. oregonense adults wer» excluded from the study since they are primarily piscivorous (Thompson, 1959). A few Ptychocheilus stomachs'examined at Wolfe Lake confirmed t h i s . Figure 10 and Table V shows the diet of juvenile Acrocheilus, M. caurinus, P. oregonense, and both juvenile and adult R. balteatus. Juvenile C. macrocheilus were excluded because t h e i r diet is-very s i m i l a r to that of the adults (as determined by the examination of a few stomachs). 40 There i s l i t t l e selection of different food items by the different species (Table V). Nearly a l l - items are shared. The major food items of young chiselmouths are often also the major food items of young P. oregonense and of a l l ages of R. baiteatus. The data from the r i v e r population were collected over a short (3 day) period and from only two locations. This introduces the p o s s i b i l i t y of having made the c o l l e c t i o n during a period of peak abundance of a p a r t i c u l a r food item, such as insects. > However, small samples from other r i v e r s suggest that the i l i m i t e d number of items found i n the guts of Okanogan River f i s h i s not a t y p i c a l ( F i g . 11, Table VI). . Adult chiselmouths caught i n the' i n l e t of Wolfe Lake during the spawning migration i n June and July, 1965. also showed a narrowing of the d i e t , i n spite of the fact that part of the sample was known to include f i s h which had fed i n part i n the lake ( F i g . 11). The guts of some of these f i s h contained items found only i n the lake. It thus seems v a l i d to conclude that i n the Okanogan River, and perhaps i n r i v e r s i n general, Acrocheilus has a much more r e s t r i c t e d diet than i t does i n Wolfe Lake. It i s noteworthy that the diets of young chiselmouths i n both the r i v e r and the lake were s i m i l a r , i n that insects and Chironomids were more important food items than was plant material. THE ABUNDANCE OF ACROCHEILUS RELATIVE TO PTYCHOCHEILUS IN RIVERS AND LAKES Since there may be some interaction occuring between Acrocheilus and Ptychocheilus (because of the s i m i l a r i t y i n the diets of the juveniles and the spawning area of.the adults), i t i s of interest t o examine the r e l a t i v e density of the two species i n the two kinds of environments (Table V I I ) . In Wolfe Lake, accurate counts of Acrocheilus and Ptychocheilus were not obtained, however i t can safely be said that Ptychocheilus w e l l outnumbers Acrocheilus. 41 Table VII* ^ e r a t i o °£ A« alutaceus to P. Oregon ens e i n lakes and rivers Location A 0 alutaceus P. oregonense Vidette Lake, B. C. Missezula Lake, B. C. Yakima River, Wash. (Patten, i 9 6 0 ) Okanogan River, W a s h * 122 246 2000 <10 23 96 4260 70 k2 In the lower Columbia River, Thompson (1959) shows that Aerocheilus i s the most important cyprinid food item of Ptychocheilus. On the basis of the above, and of data i n Table V I I , i t i s suggested that Acrocheilus , when i n r i v e r s , frequently outnumbers Ptychocheilus„ while i n lakes the reverse occurs 0 DISCUSSION In t h i s discussion the disjunct d i s t r i b u t i o n and l o c a l r a r i t y of Acrocheilus w i l l be examined i n terms of certain ecological adaptations of the species,. The present d i s t r i b u t i o n of the species can be explained as follows. After withdrawal of the Wisconsin ice sheet from B r i t i s h Columbia, Acrocheilus probably entered the Fraser drainage v i a the Okanogan River, i n whose t r i b u t a r i e s i t i s now most common i n B r i t i s h Columbia. Access t o the Eraser was possible v i a a temporary p o s t - g l a c i a l lake which connected the Nicola and Similkameen water-sheds. At a l a t e r date access was again possible v i a the Salmon River connecting the same lake to the Okanogan system. Further retreat of the ice sheet resulted i n establishment of the present drainage of the Nicola basin into the Fraser system. At a l a t e r date, access to the Fraser again resulted from the drainage of a different lake situated i n the Thompson basin and draining v i a the Salmon River into the Okanogan River. Again, further retreat of the ice exposed lower outlets to the Fraser system (Mathews, 1944)• Acrocheilus had continuous access t o the Malheur system i n Oregon v i a the Malheur River which emptied into the Columbia. Re l a t i v e l y recent volcanic a c t i v i t y blocked o f f t h i s r i v e r and isolated the entire Malheur drainage (Snyder, 1908). The d i s t r i b u t i o n of Acrocheilus over i t s range can be correlated with 43 the effects of g l a c i a t i o n . Acrocheilus i s most abundant and widespread i n warm streams with moderate current and a f a i r l y r i c h bottom f l o r a . This i s i n contrast t o the so-called " t y p i c a l trout stream", having a fast current and low tempera-ture and productivity. As a result of recent g l a c i a t i o n i n B r i t i s h Columbia, streams which favor Acrocheilus are rare and the trout type of stream predominates. In unglaciated mid-Washington and Oregon, slower, warmer streams are more common, and so i s Acrocheilus. Although northern Washington, where Acrocheilus i s common, was glaciated at the same time as B r i t i s h Columbia, the topography of the land i s more l i k e that of the unglaciated region to the south, probably because the duration of g l a c i a t i o n was less there than t o the north. While the chiselmouth does occur i n lakes, t h i s i s not common according t o the l i t e r a t u r e , and such populations are small r e l a t i v e to those of other cyprinids present. Acrocheilus seems to occur i n lakes most often i n B r i t i s h Columbia, probably as a result of the absence of suitable streams. There are several reasons for believing that Acrocheilus i s primarily adapted to a r i v e r i n e as opposed t o a lacustrine habitat. F i r s t , as has just been noted, Acrocheilus i s most abundant i n r i v e r s , and r i v e r populations are denser than are lake populations. The manner i n which Acrocheilus feeds i s c l e a r l y adapted to scraping Aufwuchs from a smooth substrate. Because of sedimentation i n a lake there may be fewer suitable s i t e s for the attachment of Aufwuchs. In contrast, r i v e r beds with current-swept bottoms often composed of stream-rounded smooth rocks provide a most suitable substrate both for the attachment of filamentous algae and for scraping by the cheselmouth. In the large aquarium i n the laboratory, a variety of different species of filamentous algae became established on the glass over an 18 month period, while no algae grew either on the mud or sand bottom. F i n a l l y , an examination of the habitats of species with mouth modifi-44 cations and diets s i m i l a r to those of Acrocheilus supports the conclusion that a scraping mouth i s especially adapted to a r i v e r i n e habitat. The Eurasian Cyprinid genus Chondrostoma contains s i x species and several subspecies. A l l of these have a lower jaw which closely resembles that of Acrocheilus 5 i n some cases, the s i m i l a r i t y i s s t r i k i n g . Berg (1948) l i s t s the habitats of a l l species as r i v e r i n e . G. V. N i k o l ' s k i i (pers. comm.) states that the diet of Chondrostoma i s algae which i s obtained by scraping from f l a t rocks i n the stream bed. A s i m i l a r example i s the Japanese salmonid, Plecoglossus. The mouth morphology of thi3 f i s h i s quite different from that of Acrocheilus, nevertheless i t does have a blunt lower jaw which i t uses to scrape algae from rocks. This f i s h also l i v e s i n r i v e r s . The habitats occupied by Acrocheilus i n the lake and the r i v e r are very d i f f e r e n t . In the Okanogan River, Acrocheilus was widely distributed over the bottom, apparently i n accordance with the d i s t r i b u t i o n of food. In Wolfe Lake, as i n most lakes, the food supply for a herbivorous f i s h i s l i m i t e d to a narrow photic zone around the margin of the lake. It i s l i k e l y that within t h i s area the amount of food available to Acrocheilus i s l i m i t e d by the amount of sui t a b l e substrate f o r the growth of algae and scraping by the f i s h . In Wolfe Lake, only sunken trees and branches appeared to provide such a substrate. It i s l i k e l y then, that a lake environment w i l l support fewer c h i s e l -mouths than w i l l a r i v e r environment of equal area. ' This w i l l be further re-ferred to when competition i s considered. I f i t i s accepted that Acrocheilus i s less w e l l adapted to lakes than t o r i v e r s , t h i s w i l l provide a p a r t i a l explanation for the unusual d i s t r i b u t i o n and abundance of the species. F i r s t , i f there are few suitable streams i t w i l l be uncommon. Secondly, when i t occurs i n lakes i t w i l l remain at a low density because less useable food i s available than i n r i v e r s . 1.5 An additional mechanism by which Acrocheilus might be excluded from otherwise suitable environments i s provided by the observation that the tempera-ture required for spawning by Acrocheilus i s higher than that required by the other l o c a l cyprinids. Although outlet temperatures of many lakes may reach 17°C, due to warming of surface waters, the outlet stream would be suitable for spawning only i f i t possessed certain characteristics such as a very slow current t o allow the return of the fry to the lake. The fact that the lake environment may provide fewer food resources for the chiselmouth suggests that i n t r a s p e c i f i c competition for food may be occurring i n Wolfe Lake and possibly other lakes. As has been discussed previously, the chiselmouth i s adapted t o scraping algae from smooth, hard sub-strat e s . Since there are probably few such areas i n Wolfe Lake, i t i s l i k e l y that the chiselmouths w i l l be forced t o compete for food i n these areas. The fact that the diet of Acrocheilus i n the lake i s much more varied than i n the r i v e r i s good evidence that i n the lake Acrocheilus i s eating items other than those which i t i s best adapted to consume. In the absence of samples of species composition of p o t e n t i a l food resources i n the lake and r i v e r , i t i s impossible t o state d e f i n i t e l y i n which environment a greater choice of items exi s t s . However, there i s no reason to assume a less varied f l o r a and fauna i n r i v e r s than i n lakes. Kendiegh (l96l) gives data which indicate that a stream of the sort i n which Acrocheilus occurs supported a more varied bi o t a than did several di f f e r e n t types of lake bottom. Nilsson (1957) found that Salmo t r u t t a had a more varied diet i n r i v e r s than i t did i n lakes. Thus i t i s probable that the chiselmouth i n Wolfe Lake i s eating a varied diet out of necessity rather than choice. That food may be i n short supply for the adult chiselmouth i n Wolfe Lake i s evidenced by the fact that as the summer progressed the diet became s l i g h t l y more specialized. Nilsson (i960) found that seasonal s p e c i a l i z a t i o n was char a c t e r i s t i c of situations where food was l i m i t i n g . This may also be related to the decrease in average fullness of the stomach of Acrocheilus from May to July, 1965 (Table II). Finally, competition for food may be the explanation for the reduced growth rate in Wolfe Lake compared with the growth rate In the Okanogan River. Chiselmouths from the Okanogan River also contained large fat deposits on the viscera, while fish of the same size, age and sex in Wolfe Lake only very rarely had such deposits. A reduction in maximum size attained as a result of a reduced growth rate may reduce the fecundity of the fish (Peppar, 1965) thus resulting in one more potential factor limiting the population density in the lake. The overlap in the diet of Acrocheilus and of the other species examined in Wolfe Lake, together with the fact that Acrocheilus seems to be feeding on items other than those i t is primarily adapted to consume, suggest that interspecific competition for food may be occurring. Larkin (1956), in a review of interspecific competition in freshwater fishes, concludes that freshwater fishes have a wide tolerance of habitats, and a f l e x i b i l i t y of feeding habits and, because of this p l a s t i c i t y , species are in general able to share many resources. Fryer (1959) has since shown that in the tropics, freshwater fishes are usually very specialized. Thus Larkin's con-clusion should be restricted to fishes In temperate regions only. Even in temperate areas, where there is interspecific overlap of diet for example, species have certain optima to which they are best adapted. When two similar species are sympatric and one or both is displaced from i t s optimal requirements, such things as a reduced growth rate or population density may result (Nilsson, 1958; Carlander, 1955). Thus, while fishes often have broad diets and can tolerate some over-lap, they are specialized to the extent that they can only show maximal growth rate and standing crop when they are not sympatric with other species having the same food or other requirements. 47 Before discussing competition involving Acrocheilus a competition among herbivores i n general must be considered,, Mayr (1963) states that general-ized herbivores are not usually food limited„ Instead, disease, and predation serve as controls of population s i z e . There are a number of reasons why t h i s may not apply t o Acrocheilus when i t occurs i n lakes,. It has already been shown that the chiselmouth i s specialized, both i n terms of diet and method of feeding. Thus Acrocheilus i s not a generalized herbivore. Diseased chiselmouths were never seen i n the f i e l d , but i t was noted previously that Acrocheilus i s extremely susceptable t o disease following injury of any sort. I t i s un l i k e l y though, that disease would hold a l l chiselmouth populations i n B r i t i s h Columbia at the same low density at the same time and for so long. The significance of predation as a mechanism regulating population . density i n lakes i s an open question. In the discussion of competition between Acrocheilus and other species t o follow, i t must be remembered that i n the absence of data concerning whether or not a given environmental resource i s l i m i t e d , a l l that can be done i s to show why Acrocheilus would be the species most c r i t i c a l l y affected i f a resource such as food were to become l i m i t i n g i n the lake. The only f i s h which would appear t o be i n direct competition with Acrocheilus are the hybrid suckers. Due to the low numbers of these f i s h i n the lake, they can not be considered serious competitors for the food of Acrocheilus. The s i m i l a r i t y of diet of the two kinds of f i s h i s probably related t o the fact that the lower jaw of the hybrids has a scraping edge sim i l a r to that of the chiselmouth. Although the diet of C_. macrocheilus p a r t i a l l y overlaps that of LB Acrocheilus, i t i s unl i k e l y that these two species feed i n the same microhabitat. This conclusion i s based on the fact that while the major components of the diet were s i m i l a r i n the two species, minor components which were very l i k e l y consumed along with the major components, were d i f f e r e n t . Unlike Acrocheilus. C. macro- cheilus probably feeds on soft, substrates such as sediment and detritus deposits. While feeding on the same thing i n different microhabitats does not necessarily prevent competition, i t could i n cases such as t h i s where the a b i l i t y of items such as filamentous algae and diatoms t o disperse i s low. M. caurinus i s primarily a crustacean feeder. At times, however, i t ' feeds on the same items as Acrocheilus. As i n the case of C. macrocheilus, M. caurinus probably feeds i n a different microhabitat from that of Acrocheilus. In summary, neither of the adults of the two more abundant species i n Wolfe Lake are i n direct competition with the chiselmouth. By feeding i n diffe r e n t microhabitats on food items having a slow rate of dispersion, i n t e r -s p e c i f i c competition i s avoided. Miura (l96l) and others (Nilsson, i n LeCren and Holdgate, 1962), have noted that the diets of young fishes of different species often overlap. In Wolfe Lake t h i s occurs with respect t o the diets of Acrocheilus and Ptycho- cheilus , and to a lesser extent., R. ba i t eat us of a l l ages. Unlike the adults, the juvenile chiselmouth has a simi l a r diet i n both Wolfe Lake and the Okanogan River. Since the diet of the young f i s h i s not as specialized as that of the adult, the juvenile chiselmouth i n the lake i s probably not at the same com-p e t i t i v e disadvantage as are the adults. Mayr (1963). states that when other things are equal and two'species occupy the same habitat, the species with the greater fecundity and l i f e span w i l l p r e v a i l . In r i v e r s i t appears that the greater p o t e n t i a l of Ptychocheilus to increase (Cartwright, 1956) i s not expressed. In lakes conditions are such that the r e l a t i v e density of the two species i s reversed,* and Ptychocheilus 49 predominates. It i s possible that the large population of juvenile squawfish l i m i t the amount of food available to the young chiselmouths. Reproduction of Acrocheilus and Ptychocheilus i n Wolfe Lake may have been complicated by the r i s e i n water l e v e l r e s u l t i n g from damming. Although both species spawn i n a part of the stream uninfluenced by the r i s e i n lake l e v e l , i t i s possible that one or both species formerly u t i l i z e d a more downstream part of the creek or the lakeshore p r i o r t o flooding of these areas, since the squawfish i s known to spawn on gravel beaches i n some lakes (K. W. Stewart, pers. comm.). In any case, the occurrence of eggs of Acrocheilus and Ptychocheilus together indicates that the two species must spawn very close t o each other at present. As i n the case of competition between juveniles for food, the large numbers of Ptychocheilus may enable i t t o crown Acrocheilus from the most suitable parts the spawning beds. While i t i s known that the two species also spawn i n close proximity t o each other i n r i v e r s , from the fact that hybrids between the two are known from r i v e r s as w e l l as lakes (Patten, I960), i t i s noteworthy that the proportion of hybrids r e l a t i v e to chiselmouths i n Patten ?s large sample was much lower than the same r a t i o i n Wolfe and Missezula Lakes (K. W. Stewart, pers. c omm.)» Laboratory observations indicate that the chiselmouth displays aggressive behavior towards individuals both of i t s own and other species. This may explain at least i n part the fact that i n the r i v e r Acrocheilus was spaced out and other species were rare. In the lake, a l l species were caught together although the adult chiselmouth did not seem t o form any sort of school, suggesting that i n both the lake and r i v e r the chiselmouth i s not gregarious. In the r i v e r , where food useable t o Acrocheilus i s abundant and other species are apparently at a1 lower density r e l a t i v e to the chiselmouth, i t i s possible, i n view of laboratory observations, that Acrocheilus i s t e r r i t o r i a l . This i s the s i t u a t i o n i n the algae-eating ayu, Plecoglos3us 0 already mentioned. 50 In lakes, on the other harid, food i s present only i n a l i m i t e d zone around the edge of the lake. Within t h i s zone, food useable t o the chiselmouth i s probably concentrated i n certain areas such as on deadfalls and drowned trees. Other species are also present i n abundance. I f the chiselmouth behaves towards other species i n the f i e l d as i t does i n the laboratory, then the lake environ-ment may subject the f i s h to considerable 3tress. Individual chiselmouths w i l l be constantly faced with maintaining distance or t e r r i t o r y i n the face of frequent int e r a c t i o n with individuals of other species, as w e l l as individuals of t h e i r own species seeking what may be a l i m i t e d food supply. The environment i n the lake may exemplify the c l a s s i c a l example of the advantages and disadvantages of t e r r i t o r i a l i t y i n different environments. In the r i v e r , the f i s h could achieve a net energy gain by defending an exclusive feeding area. In lakes, the "cost" of defence i n terms of energy might exceed the energy gained from having an exclusive feeding area. I f the behavioral cha r a c t e r i s t i c s of the chiselmouth are not f l e x i b l e enough to adapt to the lake environment by abandoning t e r r i t o r i a l behavior, then the f i s h may be subject t o one more d e b i l i t a t i n g effect. CONCLUSIONS The biology of the chiselmouth suggests several possible explanations for the unusual d i s t r i b u t i o n and abundance of the species. The adaptation of Acrocheilus resulting from the specialized mouth, to a r e l a t i v e l y warm, productive r i v e r i n e habitat, together with the p o s s i b i l i t y of requiring a warmer temperature for reproduction than other sympatric cyprinids, may explain i t s l i m i t e d occurrence i n B r i t i s h Columbia1"s cooler, faster and less productive streams. The single most important factor regulating population density of 51 Acrocheilus i n Wolfe Lake, and perhaps i n other B r i t i s h Columbia lakes, i s probably i n t r a s p e c i f i c competition for food. This results from the fact that the lake presents a l i m i t e d amount of substrate suitable for both the growth of food useable by Acrocheilus and for feeding by the method used by Acrocheilus. Inter s p e c i f i c competition for food may occur between juvenile c h i s e l -mouths and squaw f i s h , but since the a v a i l a b i l i t y of the food i s not known a d e f i n i t e conclusion can not be made. Intersp e c i f i c competition for spawning s i t e s by adult chiselmouths and squawfish may also occur. 52 LITERATURE CITED Agassiz, L. 1855. Synopsis of the ichthyological fauna of the P a c i f i c slope of North America, c h i e f l y from the collections made by the U.S. Ecpl. Exped. under the command of Capt. C. Wilkes, with recent additions and comparisons with eastern types. Amer. Jour. S c i . Arts, 2nd ser., 19:71-99. Berg, L. S. 1948. Freshwater fishes of the U.S.S.R. and adjacent countries. Smithsonian Inst., Washington. Carlander, K. D. 1955. The standing crop of f i s h i n lakes. J . Fish. Res. Bd. Canada 12(4)s543-570. Cartwright, J. W. 1956. M. S. Contributions t o the l i f e history of the northern squawfish (Ptychocheilus oregonense (Richardson)). B.A. t h e s i s , Department of Zoology, University of B r i t i s h Columbia, Vancouver, Canada. Ferguson, R. G. 1950. The f i r s t record of the chiselmouth, Acrocheilus alutaceus, Agassiz and Pickering, from B r i t i s h Columbia, Canada. Can. F i e l d Nat. 64s156. Fish, G. R. 1951. Digestion i n T i l a p i a esculenta. Nature 1675900-901. Fryer, G. 1959* The trophic interrelationships and ecology of some l i t o r a l communities with s p e c i a l reference t o the fishes, and a discussion of the evolution of a group of rock frequenting Cichlidae. Proc. Zool. Soc. Lond. 132;153-281. Gi l b e r t , C. H., and B. W. Evermann. 1896. A report upon investigations i n the Columbia River Basin, with four new species of fishes. B u l l . U.S. Fish. Comm. 14.169-204. Hynes, H. B. N. 1950. The food of freshwater sticklebacks (Gasterosteus aculeatus and Pygosteus pungitius), with a review of methods used i n studies of the food of fishes. J . Anim. Ecol. 19s36-58. Kendeigh, S. C. 1961. Animal ecology. Prentice-Hall. Englewood C l i f f s . Lark i n , P. A. 1956. I n t e r s p e c i f i c competition and population control i n freshwater f i s h . J , Fish. Res. Bd. Canada. 13(3)^ 327-342. Le Cren, E. D. and M. W. Holdgate, eds. 1962. The exploitation of natural animal populations. The B r i t i s h Ecological Society, Symposium number two. J. Wiley and Sons, Inc. New York. Mathews, W. H. 1944. G l a c i a l lakes and ice retreat i n south-central B r i t i s h Columbia. Trans. Roy. Soc. Canada 38(4)s39-57. Mayr, E. I963. Animal species and evolution. Belknap Press. Harvard. M i l l e r , R. J . 1965. External morphology of the brain and l i p s i n catostomid fishes. Copeia 45467-486. Miura, T. 1962. Early l i f e - h i s t o r y and .possible interactions of f i v e inshore species of f i s h i n Nicola Lake, B r i t i s h Columbia. Ph.D. t h e s i s , Department of Zoology, University of B r i t i s h Columbia, Vancouver, Canada. Nilsson, N. A. 1955. Studies on the feeding habits of trout and char i n north Swedish lakes. Rept. Inst. F.W. Res. Drottningholm. 36:163-225. . . 1957. On the feeding habits of "trout i n a stream of northern Sweden. Rept. Inst. F.W. Res. Drottningholm. 38?154-166. . 1958. On the food competition between two species of Coregonus i n north Swedish lakes. Rept. Inst. F.W. Res. Drottingholm.39*146-161. . I960. Seasonal fluctuations i n the food segregation of tr o u t , char and whitefish i n U+ north Swedish lakes. Rept. Inst. F.W. Res. Drottingholm. 41*185-205. Patten, B. G. i960. A high incidence of the hybrid Acrocheilus alutaceus X Ptychocheilus oregonense. Copeia Is71-73* Peppar, J. L„ I965. MS. Some features; of the l i f e - h i s t o r y of the cockscomb prickleback, Anoplarchus purperescens G i l l , M.Sc. t h e s i s , Department' of Zoology, University of B r i t i s h Columbia, Vancouver, Canada. Snyder, J. 6. 1907. Relationships of the f i s h fauna of the lakes of south-east Oregon. B u l l . U.S. Bur. Fish. 27*69-102. Thompson, R. B. 1959. Food of the squawfish Ptychocheilus oregonense (Richardson), of the lower Columbia r i v e r . Fish. B u l l . Fish and W i l d l i f e Serv. No. 158, 60s43-58. 

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